All this would be clearer if Averroes's theory were tenable, of one common human mind, or soul, one common psychic stock, as it were, sprouting out into various branches, or personalities, something like an aquatic plant, with many heads showing above water, and these distinct, but all meeting in one root under water. Then we might argue that the common stock remained infected with original sin, though individuals were cleansed. The theory is, I suppose, utterly untenable; or, if there is any truth in it, it is a truth that no man hitherto has been able to formulate without grave and dangerous error. We cannot impute such a notion to the great opponent of Averroism. But St Thomas's distinction between nature and person in this connexion would be plainer, and his whole argument more telling, on Averroistic principles. See his own remark on Averroism in Chap. XLI.
Of God and His Creatures: 4.51